Annie Leibovitz has revealed the identity of the one person whose picture she is most desperate to take - Angela Merkel.
The photographer said that without an image of the German chancellor her updated collection of influential females was missing "probably the most important woman in the world today".
But she conceded it was a tough mission, especially with Mrs Merkel under such political pressure over the migrant crisis.
"I have been trying very hard," she told BBC Radio 4's Today ahead of the opening of the new exhibition in London this week.
"I respect the fact that she doesn't want to do interviews or doesn't want to do photographs because she has other things to do.
"She is having a difficult time right now."
Leibovitz said she would like to photograph the politician - recently named the world's second most powerful person by Forbes magazine, ahead of US president Barack Obama and behind only Russian president Vladimir Putin - "in action".
"I would probably do her working. I would love to see her just at work, as I've done with Hillary Clinton. I would be respectful of her not wanting to sit for a portrait."
Leibovitz said the exhibition - an update of a project first attempted in 1999 at the behest of partner Susan Sontag - "began with women I admired and now has turned a little bit more into trying to gather subjects as we go along.
"Obviously it's a project that will never be done but it is interesting to stop now, 17 years later, and take a look at where we are now."
The exhibition Women: New Portraits opens on January 16 at Wapping Hydraulic Power Station, the first leg of a world tour.